Using MOSFETS with TTL levels (5 Volt and 3.3 Volt)

Various Arduino projects that need to switch a high DC load are using MOSFET’s to do this, according to the circuit at the right (R1 is optional and may be necessary to switch off the FET if the pin goes low.

Popular MOSFET’s that are used are the IRF510 and IRF 520

IRF510

IRF520

Looking at those graphs one can see that at a gate to source level of 5V (Arduino levels) the IRF510 is only capable of delivering 1 Amp, whereas it is specified for 5,6 Amps continuous current. The 520 is somewhat better: at 5 V it delivers 3 Amps from its max of 9.2. This is because these FET’s are designed to pass the max current at gate voltages of around 10 Volts and that is beyond what most microcontrollers can deliver.